The main objective of this research is to make detailed investigations of the human electroretinogram using the method of stimulus alternation. An attempt will be made to use stimulus conditions which will facilitate the comparison of the results with data obtained with other forms of visual experimentation. An advantage of the method of alternation is that it permits quantitative studies of responses under conditions where the problems of stray light and other sources of error are minimized. A number of specific experiments are planned. An effort will be made to interpret the results they provide in terms of photopic and scotopic mechanisms, differences in the relative density of cones and rods in different parts of the visual field, and response additivity. Experiments are planned in which special sensitivity will be determined at different sites on the retina, in which a determination will be made of the importance of the texture of the stimulus at different retinal locations, in which the pulse-cycle ratio and the alternation rate are varied at different levels of adaptation. Most experiments will be conducted with normal human subjects. Some data will be collected on patients having localized defects of their visual fields.